MS101 Lesson 04: Basic Map Reading — Comprehensive Study Notes (Maps, Grids, Scales, Directions, Equipment, Elevation)

Chapter 2 — Maps

  • Cartography: the art and science of expressing known ground features graphically by maps and charts.
    • Origins: unknown who drew the first map; military needs drove mapping accuracy and detail.
    • Modern importance: essential for reading/interpreting maps to move quickly and effectively on the battlefield.
  • Definition of a map (2-1):
    • A map is a graphic representation of a portion of the earth’s surface drawn to scale, viewed from above.
    • Uses colors, symbols, and labels to represent ground features; ideal shape of every feature is not feasible.
  • Map readability (2-2 to 2-3):
    • Features are shown with conventional signs and symbols; many symbols are exaggerated for legibility.
    • NGA guidance determines feature portrayal and symbol choices.
  • Purpose of maps (2-4):
    • Show existence and distance between ground features (populated places, routes, etc.).
    • Indicate terrain variations, natural feature heights, and vegetation extent.
    • Support planning for movement, logistics, and employment of forces far from home bases.
    • Emphasize that maps are only valuable if users can read them.
  • NGA products and map categories (2-8 to 2-9):
    • Four NGA product categories: hydrographic, topographic, aeronautical, and digital.
    • Types of maps: planimetric (horizontal positions only), topographic (with relief via contours), digital maps, digital city graphics, controlled image base, compressed arc digitized raster graphics, and digital terrain elevation data (DTED).
    • DTED levels defined by sample spacing:
    • DTED0DTED0: ~1000 m spacing
    • DTED1DTED1: ~100 m spacing
    • DTED2DTED2: ~30 m spacing
    • Other NGA products: TalonView (mapping application with overlays), vector maps (VMap Levels 0–2), photomap, joint operations graphics, photomosaic, terrain model, military city map, special maps (terrain, drainage, vegetation, climate, coasts/landing beaches, roads/bridges, railroads, airfields, urban areas, electric power, fuels, water resources, groundwater, construction materials).
  • Military map substitutes (2-7 to 2-11):
    • If NGA maps aren’t available, substitutes include foreign maps, atlases, geographic maps, tourist road maps, field sketches.
    • NGA can provide black-and-white reproductions of foreign maps or base maps on intelligence.
    • Foreign maps require marginal information adjustment and symbol interpretation; accuracy varies; use legends.
    • Atlases and geographic maps provide general information; foreign or tourist maps may be used with caution.
    • Geographic/GEOREF considerations and field sketches may serve in a pinch.
  • Standards of accuracy (2-12):
    • NGA sets accuracy standards; unless marginals specify otherwise, treat maps as meeting accuracy requirements.
  • Marginal information and symbols (Chapter 3 overview)
  • Marginal information begins every map: readers should examine margins for critical data before using the map.
  • Core marginal items (3-1 to 3-3):
    • Sheet name (1)
    • Sheet number (2)
    • Series name (3)
    • Scale (4)
    • Series number (5)
    • Edition number (6)
    • Index to boundaries (7)
    • Adjoining sheets diagram (8)
    • Elevation guide (9)
    • Declination diagram (10)
    • Bar scales (11)
    • Contour interval note (12)
    • Spheroid note (13)
    • Grid note (14)
    • Projection note (15) and the three projection types for military maps (Transverse Mercator; Lambert Conformal Conic with specified parallels; Polar Stereographic)
    • Vertical datum note (16)
    • Horizontal datum note (17)
    • Control note (18)
    • Preparation note (19)
    • Printing note (20)
    • Grid reference box (21)
    • Unit imprint and symbol (22)
    • Legend (23)
  • Additional marginal items (3-2 and after): glossary, classification, protractor scale, coverage diagram vs reliability diagram, special notes (24), user’s note (25), stock number identifications (26), conversion graph (27).
  • Topographic map symbols (3-3 to 3-5):
    • Legend contains standard symbols; symbols are designed to resemble features from above; road/feature exaggerations may occur.
    • Mapmaker (cartographer) uses symbols to represent natural/man-made features; features are centered on true location unless preserving road relations requires shifting some features.
  • Military symbols (3-6):
    • Not normally printed on standard maps due to mobility and security; used on overlays and military maps; refer to FM 1-02 for more information.
  • Colors on a military map (3-7):
    • Black: cultural/man-made features (buildings, roads, surveyed elevations, labels).
    • Red-Brown: cultural features, relief features, non-surveyed elevations, contour lines on red-light readable maps.
    • Blue: hydrography (water features).
    • Green: vegetation with military significance (woods, orchards).
    • Brown: relief features and elevation on older maps; cultivated land on red-light readable maps.
    • Red: populated areas, main roads, boundaries (on older maps).
    • Other colors: used for special information as noted in marginal information.
  • Chapter 4 — Grids (overview)
  • Purpose and reference systems (4-1 to 4-2):
    • Geographic coordinates form the basis of global location: parallels (latitude) run east-west; meridians (longitude) run north-south.
    • Prime meridian at Greenwich; latitude measures north-south from the equator; longitude measures east-west from the prime meridian.
  • UTM/UPS and grid fundamentals (4-11 and nearby):
    • Grid systems divide the earth into 6°x8° quadrangles; each 100,000-m square is identified by a two-letter code within a grid zone.
    • Regular grid lines divide the 100,000-m square into 10,000-m, 1,000-m, 100-m, and 10-m intervals depending on map scale.
    • Principal digits are printed at ends of grid lines to aid quick reference; two-digit principal digits identify the major grid line; smaller digits complete the 10,000/1,000 digit values.
  • Locating within grid systems (4-12 to 4-16):
    • Grid coordinates are read right (easting) then up (northing).
    • 100,000-m square identification appears in the grid reference box; if a sheet spans multiple 100,000-m squares, the separating grid lines are shown with letters identifying the squares (e.g., GL, FL).
    • The 1:50,000/1:100,000/1:25,000 scales use 10,000-m and 1,000-m index lines; 10,000-m lines are heavier on larger-scale maps.
  • 100,000-m, 10,000-m, 1,000-m, 100-m, and 10-m grids (4-16 to 4-25):
    • 100,000-m square: two-letter designation locates the larger area (e.g., 16S).
    • 10,000-m square within the 100,000-m square is identified by two digits; 1,000-m squares and 100-m or 10-m graduations further refine position.
    • Reading scales and grid references depend on map scale; the 1:50,000 map subdivides a 1000-m grid block into 100-m blocks, etc.
  • Grid reference box (4-25 to 4-27) and GEOREF (4-26 to 4-27):
    • The grid reference box shows the grid zone designation and 100,000-m square on the left; the right side explains how to use the grid in the sample 1000-m square.
    • GEOREF (World Geographic Reference System): worldwide position reference, divided into 24 longitudinal zones and 12 latitudinal bands; a 4-letter code identifies a 1° quadrangle, which can be extended to 4 letters + 6 numbers for smaller divisions (0.1″ quadrangles).
  • Other grid systems (4-18 to 4-20): British grids (phased out for NGA UTM); GEOREF details; etc.
  • Protection of map coordinates (4-21): use authorized low-level numerical codes to prevent easy interception of locations.
  • Chapter 5 — Scale and Distance (RF and distance conversion)
  • Representative Fraction (5-1 to 5-3):
    • RF is the numerical scale; the map distance is the numerator (MD) and ground distance is the denominator (GD):
    • RF = rac{MD}{GD}
    • RF is independent of units; e.g., 1:50,000 means 1 unit on map equals 50,000 units on ground.
    • Ground distance from a map distance: GD=MDimesextdenominatorGD = MD imes ext{denominator}
    • Example: map distance MD = 5 units on a 1:50,000 map → GD=5imes50,000=250,000GD = 5 imes 50{,}000 = 250{,}000 units on ground.
  • Metric system basics (5-3):
    • 1 m = 100 cm; 100 m = 1,000 m? (clarify: 100 m = 0.1 km; 1,000 m = 1 km; 10,000 m = 10 km).
    • Appendix E contains unit conversions.
  • RF determination without a known RF (5-4 to 5-6):
    • Compare map distance MD to known ground distance GD between two points; compute RF via RF = rac{MD}{GD} (MD and GD must be in same units).
    • If using another map with known RF, match points, measure MD, use GD from the known map, and solve for RF with RF = rac{MD}{GD}.
    • Sometimes you can compute ground distance from a known RF and map distance using the same formula.
    • Note: as scale decreases (smaller features on map), measurement accuracy decreases because features are exaggerated for readability.
  • Graphic (bar) scales (5-7 to 5-12):
    • A graphic scale is a ruler printed on the map; multiple scales may be present for different units.
    • To measure straight-line distance: place a straight edge across the two points and mark the edge at the points; align with the primary (whole units) scale and extension scale to read distance.
    • Reading: read the primary scale for whole units, then extension scale for increments; extension scale increases from right to left.
    • For curved lines (roads/streams), use the edge of a paper and place tick marks at start and end points; the curved distance is read by transferring to the graphic scale.
  • Time-distance scales (5-16 to 5-18):
    • Build a time-distance scale to estimate travel time: R = rate of travel, T = time, D = distance; T = rac{D}{R}
    • To construct a time-distance scale: compute map distance for a given ground distance, draw a line of that length on the map, subdivide into time increments, and create an extension scale for smaller units.
  • Other distance methods (5-19 to 5-20):
    • Pace count: count paces to cover 100 m; determine pace count using a measured course of 100–600 m.
    • Pace, timing, and pacing are alternative methods when map scales cannot be used.
  • Practical note: distances on maps are flat distances; real ground distances are affected by terrain and elevation runoff; factor in this difference during navigation.
  • Chapter 6 — Directions (azimuths and north references)
  • Base lines (6-2):
    • North references include True North (TN), Magnetic North (MN), and Grid North (GN).
    • True North is the line from a ground point to the North Pole; MN is the direction of the magnetic pole; GN is defined by vertical grid lines on the map.
    • Declination changes over time; NOAA provides a magnetic field calculator for current declination values.
  • Declination and declination diagram (6-10 to 6-13):
    • Declination diagram shows relationships among grid north, magnetic north, and true north; typical data include Grid-Magnetic (G-M) angle, Grid convergence, and conversion notes.
    • G-M angle is the angular difference between grid north and magnetic north; convert azimuths using this angle.
    • Grid convergence is the angle between true north and grid north; used for converting between true/grid/magnetic azimuths at the sheet center.
    • Conversion notes explain how to add or subtract the G-M angle depending on whether the declination is easterly or westerly; see Table 6-1 (not provided here).
    • Caution: declination diagrams older than ~20 years may have unreliable magnetic readings; verify current values.
  • Azimuths (6-3 to 6-4):
    • An azimuth is a horizontal angle measured clockwise from a north base line (TN, MN, or GN).
    • Back azimuth is the opposite direction (+/- 180° depending on the azimuth value).
    • No negative azimuths on the azimuth circle; 0° is equivalent to 360°.
  • Grid azimuths and protractor use (6-4 to 6-9):
    • When plotting an azimuth on a map, use a protractor to measure the angle between grid north and the line joining two points.
    • Base line alignment is critical; two checks ensure proper alignment: align the base line with a known north-south grid line and confirm with equal counts from 0° and 180° marks.
    • Protractor use requires placing the index at the line’s crossing with a north-south grid line; the line of sight is read from the scale; read to nearest degree or 10 mils.
  • Protractor types (6-5 to 6-6):
    • Types include full circle, half circle, square, and rectangular; all divide the circle into angular units with an outer scale and an index mark.
    • The military protractor (GTA 5-2-12) has two scales: inner (degrees) and outer (mils); 0–180° is a base line; index aligns with the azimuth line.
  • Plotting and reading azimuths (6-7 to 6-9):
    • To plot an azimuth: place the protractor with the index at the intersection of the azimuth with a north-south grid line; align base line with the grid line; read the grid azimuth from the scale.
    • For accuracy checks, verify base line alignment by re-reading from the grid line.
  • Declination conversion basics (6-10 to 6-15):
    • Conversion between grid and magnetic azimuths uses the G-M angle and the declination diagram; the direction to add or subtract depends on whether declination is easterly or westerly.
    • Always ensure reading is from the starting point to the ending point on the map for grid azimuths; mid-points can produce opposite readings if read from the wrong end.
  • Practical note on azimuths (6-15):
    • There are no negative azimuths; 0° and 360° are identical points on the circle.
  • Chapter 8 — Navigation Equipment and Methods (compasses and GPS)
  • Types of compasses (8-1 to 8-2):
    • Lensatic compass is the most common; M2 compass is a specialized artillery compass; wrist/pocket compass is lightweight; a protractor can be used when a compass is not available (but only grid azimuths can be obtained from a map using a protractor).
  • Lensatic compass components (8-2):
    • Cover protects the floating dial; sighting wire and luminous sighting slots for night navigation.
    • Base contains:
    • Floating dial with E/W marks; arrow points to magnetic north.
    • Outer mil scale and inner degree scale (often red).
    • Fixed index line under a glass cover; bezel ring with 120 clicks; luminous line for navigation; thumb loop; lens with rear sight for sighting objects.
  • Handling and care (8-3 to 8-6):
    • Check floating dial, sighting wire, glass/crystal, legibility, and dial smoothness; ensure no sticking.
    • Separation distances: high-tension power lines ≈ 55 m; field guns/vehicles ≈ 18 m; telegraph/telephone/barbed wire ≈ 10 m.
    • If compass shows >3° deviation, do not use for navigation; re-check on a known line of direction.
    • When folded, ensure rear sight locks down on bezel to protect dial.
  • Using a compass (8-7 to 8-11):
    • Centerhold technique: rotate body to point at the object; read azimuth under fixed index line; preferred for speed, visibility, terrain, and when a rifle is in use.
    • Compass-to-cheek technique: sight object with front sight, then read dial through eye lens; used primarily for sighting.
    • Presetting and following an azimuth: hold the compass level, rotate until azimuth lines up under the fixed index line, align bezel so luminous line aligns with magnetic north arrow, then follow with centerhold technique toward the front sight wire.
  • Chapter 9 — Elevation and Relief
  • Elevation and relief concepts (9-1 to 9-2):
    • Datum plane (mean sea level) is the reference for vertical measurements.
    • Elevation: vertical distance of a point above/below mean sea level.
    • Relief: representation of terrain shapes (hills, valleys, streams, etc.). Digital terrain is data-driven and depends on device/software; digital terrain models (DTM/DEM) represent terrain, with or without man-made/vegetation features.
  • Depicting relief methods (9-3 to 9-8):
    • Layer tinting: color bands indicating elevation ranges; allows quick reading but not exact elevations.
    • Form lines: dashed lines showing general relief without fixed elevations.
    • Shaded relief: tonal shading to emphasize slope; often used with contours.
    • Hachures: short lines indicating relief, useful for mountainous regions (not precise elevations).
    • Contour lines: primary method; connect points of equal elevation. Types:
    • Index contours: every 5th contour line is heavier and labeled with its elevation.
    • Intermediate contours: finer lines between index contours, no labels.
    • Supplementary contours: dashed lines indicating smaller elevation changes (often at half the contour interval).
  • Contour intervals and elevation calculation (9-9 to 9-12):
    • Determine contour interval and unit (meters, feet, etc.) from marginal information.
    • Locate the nearest index contour line and determine whether elevation increases or decreases.
    • To find exact elevation of a point between contours: add multiples of the contour interval to the nearest index contour line as you cross intermediate lines.
    • For a hilltop without survey marker, estimate by adding half the contour interval to the last index contour line.
  • Between-contour elevation estimation (9-3 to 9-5):
    • If between contour lines is less than one-fourth of the interval, elevation equals the lower contour line.
    • If between is between one-fourth and three-fourths, add half the contour interval to the lower contour line.
    • If more than three-fourths, elevation is at the next contour line up.
  • Depressions, hills, and other terrain features (9-12 to 9-19):
    • Depression: low point; represented with contour lines that close and tick marks pointing toward lower ground; subtraction of half the contour interval may be used to locate bottom.
    • Hill: concentric contour lines; innermost closed contour indicates hilltop.
    • Saddle: dip between two higher grounds; often hourglass-shaped; three directions toward high ground and one toward low ground.
    • Valley: U- or V-shaped contour lines; water flows from high to low ground; the closed end points upstream.
    • Ridge: long high ground; centerline typically shows lower ground on three sides but may be flat; contour lines tend to be U- or V-shaped and point away from high ground.
  • Major terrain features (9-26): hills, saddles, valleys, ridges, depressions; with definitions and map representations.
  • Minor terrain features (9-32): draws, spurs, cliffs; descriptions and how they appear on maps.
  • Supplementary features (9-36): cuts and fills; man-made features affecting elevation and representation.
  • Terrain interpretation (9-38): terrain features should be interpreted in relation to contour shapes, ridgelining, and streamlining to understand exposure, movement, and line of sight.
  • Practical implications: elevation and relief influence movement, cover, fire control, and planning; accurate reading of terrain features is essential for effective command and control.